The present invention concerns a coin insert for the firing deck of a combustion chamber in an internal combustion engine. More specifically, the invention concerns means for strengthening and supporting the insert and for supporting the insert to permit expansion due to thermal loads.
During normal operation of various types of internal combustion engines, the surfaces of certain of the components of the engine defining the combustion chamber, attain temperatures within the range of 1500-1800.degree. F. Such temperatures prohibit the use of conventional sealing methods and can cause metals to become inherently weak. The heat of combustion within the combustion chamber can cause inordinate thermal loads to be imposed on the engine block or more specifically the firing deck at the cylinder head. The thermal stresses caused by the intense heat in the combustion chamber frequently cause distortion and/or cracking of the firing deck of the cylinder head so that a new head is required or so that the cracks must be sealed and machined for reuse. Moreover, heat loss through the walls of the cylinder or through the cylinder head can lead to waste of a substantial amount of the energy produced by combustion.
To preclude and/or minimize these problems, coin inserts have been used to protect the firing deck area of the engine body, and particularly the cylinder head. In this instance, the exposed face of the insert constitutes the firing deck which is subjected to the greatest heat generated during the operation of the engine. The coin or firing deck insert then absorbs the lion's share of the thermal stresses associated with the heat of combustion, thereby insulating the cylinder head from the high thermal loads.
The patents to Heydrich et al., U.S. Pat. Nos. 4,328,772 and 4,344,390, owned by the assignee of the present invention, disclose one type of coin insert or end piece. The end piece disclosed in these patents is mechanically restrained between the cylinder head and the cylinder liner of the engine block. Radial clearance is provided around the periphery of the end piece to permit radial expansion during high-temperature conditions. One problem associated with end pieces according to either of these references is that the end piece can endure excessive deflection and cyclic loading due to injector forces, and the forces of combustion and thermal expansion. This excessive deflection or cyclic loading can lead to fatigue failure of the end piece.
The patent to Spencer, U.S. Pat. No. 4,112,906, shows a firing deck insert for an internal combustion engine which includes a boss that is threaded into the cylinder head to support the insert. The configuration of the firing deck insert in Spencer requires a certain amount of precision machining for the firing deck insert. Moreover, there is no provision in this reference of some means for sealing around the valve openings in the insert.
There is a need for a coin or firing deck insert which is capable of absorbing the thermal heat and thermal loads associated with combustion in the engine cylinder. The need extends to a coin insert that is configured to handle the high cyclic loads imposed on the firing deck and at the fuel injector. The insert should be relatively simple to machine and install, while still providing the benefits of prior coin inserts.